Blood Spatter Analysis Lecture - part 1

Summary

This lecture delves into the intricate field of blood spatter analysis, a crucial forensic technique. It covers how blood patterns reveal information about the crime, such as weapon type, number of blows, and victim position. The talk introduces various detection methods, including light sources, presumptive tests, and reagents like luminol and phenalene. It also explores the significance of blood spatter patterns, the physics of blood drop formation, and the use of trigonometry to determine angles of impact, ultimately helping to identify the crime's point of origin.

Takeaways

• 🔎 Blood Spatter Analysis (BSPA) examines patterns of blood stains to determine various aspects of a crime scene.
• 🚔 Forensic scientists can deduce information such as the type of weapon used, the speed of the weapon, the number of blows, and the position of the assailant and victim.
• 🕵️‍♂️ Different techniques are used to detect blood, including specific light sources and filters, presumptive tests, and reagents like phenalene and heem sticks.
• 💡 Luminol is a chemical that reacts with blood to create a blue glow, useful for revealing blood stains that are not visible to the naked eye.
• 🚫 Bleach can interfere with the detection process, as it reacts with certain chemicals used for blood detection, leaving a smudge instead of a glow.
• 💚 Florene is another chemical that can be used for detecting fine blood stains, causing them to glow greenish-white.
• 📸 Crystal Violet is used for creating a purple color in blood stains for photographic documentation, helping to identify shoe types and footprints.
• 🔍 Blood stain patterns are categorized by the force applied, such as low, medium, or high velocity spatters, and can indicate the direction of the blood flow.
• 📏 The size and shape of blood drops can provide information about the distance and angle of the blood drop, influenced by factors like the volume and the surface it falls on.
• 📐 Trigonometry is used to calculate the angle of impact from blood drops, with measurements of width and length plugged into a spreadsheet for precise calculations.
• 📍 The point of origin and area of origin can be determined by analyzing the pattern and direction of blood spatters, converging to the point where the incident occurred.

Q & A

What is the main focus of the lecture?

The lecture focuses on blood spatter, discussing the patterns that blood stains present on different surfaces and the techniques forensic scientists use to detect and analyze them.

What does BSPA stand for in the context of the lecture?

BSPA stands for Blood Stain Pattern Analysis, which is a method used by investigators to analyze the patterns of blood spatter at crime scenes.

What can forensic scientists deduce from blood spatter analysis?

Forensic scientists can deduce the type of weapon used, the speed of the weapon, the number of blows, the handedness of the assailant, the position of the victim, the sequence of wounds, the movement of the assailant, and the time of death from blood spatter analysis.

What are the different light sources that forensic scientists might use to detect blood?

Forensic scientists may use different light sources such as a flashlight with a particular filter or UV lights to make blood stains visible that are not visible to the naked eye.

What is a presumptive test in the context of blood detection?

A presumptive test is a chemical test that reacts with the properties of hemoglobin to indicate the presence of blood, but it does not confirm if the blood is human.

What is the purpose of using phenalene or a heem stick in blood detection?

Phenalene or a heem stick are reagents used to swab a surface; if blood is present, the swab turns pink, indicating the presence of blood.

What is the chemical luminol used for in blood detection?

Luminol is a chemical used in blood detection that glows blue when sprayed on a surface, revealing blood stains that are not visible under normal lighting conditions.

What is the difference between a transfer and a contact blood stain pattern?

A transfer blood stain pattern occurs when blood is wiped or smeared onto a surface, while a contact pattern is created by direct contact between the blood source and the surface.

What is stringing and how is it used in blood spatter analysis?

Stringing is a technique used in blood spatter analysis where a string is run through elliptical blood drops to determine the direction of the blood flow and to help identify the origin of the blood spatter.

How do forensic scientists determine the angle of impact from a blood drop?

Forensic scientists use trigonometry to measure the width and length of a blood drop, calculate the sine of the angle, and determine the angle of impact.

What is the significance of the point of convergence in blood spatter analysis?

The point of convergence is where lines drawn through the elliptical blood drops intersect, indicating the area or point of origin of the blood spatter, which helps in understanding the crime scene dynamics.

How does the height of a blood drop affect its size and the resulting spatter pattern?

The height from which a blood drop falls affects its speed and, consequently, its size and the diameter of the resulting spatter pattern. The higher the drop, the larger the diameter, until it reaches a maximum due to air resistance.

What factors influence the shape of a blood drop when it hits a surface?

The shape of a blood drop when it hits a surface is influenced by the volume of the drop, the speed at which it falls, and the type of surface it lands on, such as smooth glass or rough cardboard.

What is the significance of spines in blood drop analysis?

Spines are elongated extensions from the main drop that can indicate the height from which the drop fell and the type of surface it landed on, providing clues about the crime scene.

How do forensic scientists use the shape of blood drops to determine the direction of flow?

Forensic scientists look at the shape of blood drops, particularly the elongated droplets, to determine the direction of flow. The tail of the droplet points in the direction the blood was traveling when it fell.